Abstract

A stream of substrate pentachlorophenol [PCP, 5 mg min⁻¹ in water–methanol (1 + 4, v/v)] was merged with 1.5 ml min⁻¹ of supercritical carbon dioxide (scCO₂) and delivered to a reactor column (25 cm × 1 cm) of zero-valent palladium–magnesium mixture. The resulting dechlorinations, although very efficient, were not quantitative. For continuous operation at 400 °C for 6 h, phenol was the principal product, with lesser quantities of methylated products and only traces of chlorinated products (principally monochlorinated species). PCP deoxygenation was not observed and ring methylation was decreased relative to analogous reactions in hydroxylic organic solvent. With time, the reactor column slowly lost dechlorination activity. Reducing the loading of Pd⁰ on Mg⁰ from 2% to 1% (w/w) apparently did not change the course of the reaction; however, the dechlorination capacity was decreased correspondingly. None the less, over 6 h or 5 h of continued operation, the dechlorination efficiency was 0.995 for the 2% (w/w) loading of Pd⁰ on Mg⁰ and 0.984 for the 1% (w/w) loading.